A problem frequently encountered in catalyzed processes is the relatively short life of the catalysts, e.g. in hydrotreating processes especially when employing heavy feedstocks such as residua. In such a process the relatively high concentrations of asphaltenes and/or asphaltic components normally present in such feedstocks, tend to result in excessive coke formation and deposition thereof on the catalyst, thereby reducing the active catalyst surface and hence the overall catalytic activity.
In recent years a considerable effort has been spent on finding ways and means of extending the catalyst life, especially because of the increasing tendency to use heavier feedstocks.
A proposal towards solving the problem of reduced catalyst life as a result of coke and/or metal deposition on the catalyst, has been described in U.S. Patent Specification No. 4,378,308, filed Mar. 29, 1983, and comprises coating the catalyst surface with a hydrated clay mineral, hydrated alumina, hydrated silica or mixtures thereof. It is postulated that such a coating, which generally has a smaller pore size than the original catalyst, protects the catalyst by inhibiting the diffusion of catalyst poisons to the active sites. A thus prepared catalyst can be considered to be a catalyst having a non-uniform distribution of the active component i.e. a catalyst comprising a relatively large core containing all the active component, covered by an active component-free outer shell.
Although the thus prepared catalysts are likely to be less sensitive to contamination by certain feedstock components or derivatives thereof, they still possess a number of inherent disadvantages. For instance they will suffer from adhesion problems at the interface of the coating and the original catalyst, which will reduce the overall mechanical strength of the coated catalyst. Furthermore, the mechanical strength of the coating as such may be inferior to that of the original catalyst and may thus give rise to excessive attrition. By coating an existing catalyst it will be very difficult to maintain the original shape of the catalyst, which may be especially critical in the case of spherically shaped catalysts or catalysts based on carriers having a very specific shape such as trilobes and rings. Finally the actual coating of an existing catalyst introduces an additional preparation step.
Hence it will be clear that there is room for improvement in the preparation of catalysts for use in processes wherein catalyst contamination and/or poisoning is likely to occur.
It is now proposed to prepare metal-containing supported catalysts by a single step process wherein the combination of process conditions and nature of the reactants will determine the ultimate distribution of the metal or metal compound over the support. This process results in supported catalysts which do not suffer from the inherent disadvantages of the catalysts referred to hereinbefore.